1. Field of the Invention
The present invention relates to a sheet supply apparatus used with an image forming apparatus such as a printer, facsimile machine, copying machine and the like and adapted to supply a sheet from a sheet containing device containing sheets such as originals, recording sheets or the like.
2. Description of the Related Art
In conventional sheet supply apparatuses used with image forming apparatuses such as printers, for example, a sheet cassette as a sheet containing device containing a plurality of sheets can be removably mounted to the apparatus and a sheet can be supplied from the mounted sheet cassette to an image forming station for forming an image by a sheet supply roller.
An example of such conventional sheet supply apparatuses is shown in FIG. 8. The conventional sheet supply apparatus will be explained with reference to FIG. 8.
A sheet supply apparatus A is arranged below an image forming apparatus B. The sheet supply apparatus A is designed so that a sheet cassette (sheet containing device) 1 for containing sheets can be mounted between two opposed side walls of a body 2 of the apparatus. Support portions 2a, 2b for guiding the insertion of the sheet cassette 1 into the body 2 and for supporting the sheet cassette 1 are protruded from and formed on the side walls of the body 2.
Further, the sheet cassette 1 comprises a box-shaped cassette body 6, a pivotable intermediate plate 16 on which a plurality of sheets are stacked, and pressure springs 15 for biasing the intermediate plate 16 toward a sheet supply roller 11 to urge the sheet stack P against the sheet supply roller 11. The cassette body 6 is provided with engagement portions 6a, 6b protruded outwardly from side walls thereof. By engaging these engagement portions 6a, 6b with the support portions 2a, 2b of the body 2 of the sheet supply apparatus, the sheet cassette 1 is removably guided into the body 2.
Incidentally, a positioning guide 17 is formed on an undersurface of a partition 2c of the body 2, which positioning guide 17 serves to position the sheet cassette 1 with respect to the body 2 of the sheet supply apparatus in a widthwise direction of the sheet (left and right direction in FIG. 8) by engaging a guide projection 6c formed on the cassette body 6 with the positioning guide 17.
A sheet positioning member 3 for regulating one side edge of the sheet stack P to position the sheet stack in the widthwise direction of the sheet is secured to a bottom of the cassette body 6, and a sheet urging member 9 for biasing the sheet stack on the intermediate plate 16 against the sheet positioning member 3 is provided on an auxiliary positioning member 5 at an opposite side. The sheet urging member 9 may comprise a plate-shaped member biased by a spring to urge the sheet stack P, or may comprise a leaf spring for urging the sheet stack directly as shown in FIG. 8.
According to this sheet positioning arrangement, the sheet stack P is positioned with respect to the cassette body 6 in the widthwise direction of the sheet, by urging one side edge of the sheet stack P on the intermediate plate 16 by the sheet urging member 9 so that the other side edge of the sheet stack is abutted against the sheet positioning member 3.
In this way, the sheet stack P is positioned with respect to the cassette body 6 in the widthwise direction of the sheet by the sheet positioning member 3 and the sheet urging member 9, and, further, the cassette body 6 is positioned with respect to the body 2 of the sheet supply apparatus in the widthwise direction of the sheet by the positioning guide 17 of the body 2 and the guide projection 6c of the cassette body 6. Accordingly, the sheet stack P is positioned with respect to the body 2 of the sheet supply apparatus in the widthwise direction of the sheet.
However, the above-mentioned conventional sheet supply apparatus has the following disadvantages.
Since the sheet positioning member 3 is secured to the bottom of the cassette body 6 so that it extends perpendicularly to the bottom, when the sheets are stacked in the sheet cassette, the bottom of the cassette body 6 is flexed or deformed by the weight of the sheets, with the result that the sheet positioning member 3 is inclined as shown in FIG. 8. That is to say, the sheet positioning member 3 for positioning the sheet stack P in the widthwise direction of the sheet is inclined in accordance with the amount of sheets P stacked on the intermediate plate 16 to change the perpendicularity of the member 3 greatly. As a result, the sheet stack P is positioned by abutting one side edge of the sheet stack against the inclined sheet positioning member 3.
Accordingly, when the amount of the sheets P stacked in the sheet cassette is little, since the deformation of the bottom of the cassette body 6 is also small, the sheets P can be supplied at the predetermined widthwise position. However, if the amount of the sheets P stacked in the sheet cassette is large, the deformation of the bottom of the cassette body 6 is also large, and, accordingly, the sheet positioning member 3 is inclined greatly, with the result that the widthwise position of the positioned sheet stack is considerably offset from the predetermined position, thus making the correct positioning impossible.
Incidentally, if the deformation of the bottom of the cassette body 6 is suppressed, the above problem can be eliminated. However, to achieve this, if the rigidity of the cassette body 6 is increased, the weight of the sheet cassette will be increased to make the handling of the cassette difficult, to make the construction complicated and to make the cassette expensive.